In one type of known hydraulic elevator, either a single hydraulic jack, positioned below the elevator car, or a pair of hydraulic jacks, located on opposite sides of the car, are connected to the car frame for raising and lowering the car between floors. In the case of a single jack elevator, the upper end of the plunger is connected to the underside of the car frame. In the case of a dual post elevator, the upper ends of the plungers are connected to the top of the car frame. The principal advantage of a dual jack elevator is that it does not require providing a jack hole below the elevator car, which is some installations is impractical. Dual post elevators, however, are generally more limited in the range of upward car travel which is available.
Hydraulic elevator systems are also known where, instead of connecting the plunger or plungers directly to the car frame, the plungers are coupled indirectly to the car frame by a rope and sheave arrangement to support the car and its load. Such an elevator is referred to as a roped hydraulic elevator.
The most common design for roped hydraulic elevators with capacities greater than 3,000 pounds is to use a pair ofjacks, located on opposite sides of the car. One jack is mounted on each side of the car adjacent to the car rails. A set of rails is required for each jack. A sheave is mounted on top of each jack. The ropes are attached to each side of the car, pass over the sheaves mounted on top of the jacks, and are attached to the pit floor.
This arrangement produces a 2:1 ratio of car travel to jack travel. However, the use of two hydraulic jacks requires the shaft to have a larger cross-sectional area, i.e., to accommodate both jacks and the car, and requires that the rails be designed with the capacity to absorb larger guide shoe loads caused by any hydraulic imbalances between the jacks.
There have also been proposals for roped hydraulic elevators which operate with only a single hydraulic jack. An example of such a roped hydraulic elevator is disclosed in U.S. Pat. No. 4,977,980. The hydraulic jack is located to one side the elevator car and has its cylinder end fixed relative to the shaft floor. A sheave is secured to the upper end of the plunger, and a pair of sheaves are secured to the underside of the car frame, on opposite sides thereof A rope has one of its ends secured to a beam located at the upper end of the elevator shaft, on the side of the car opposite to the jack. The rope extends downwardly to one of the car-mounted sheaves, crosses underneath the car to the other car-mounted sheave, and then continues upwardly to the sheave on top of the plunger. Thereafter, the rope extends downwardly, parallel to the jack, and is secured the shaft floor. When the jack plunger extends and retracts, the elevator car moves up and down.
U.S. Pat. No. 5,443,140 discloses a roped hydraulic elevator which is similar to U.S. Pat. No. 4,977,980 except that the second end of the rope, after passing under the elevator car and over the plunger-mounted sleeve towards the shaft floor, is not secured to the shaft floor. Instead, the rope passes under another sheave mounted at the base of the plunger, extends upwardly and around a second sheave mounted on top of the plunger, and finally extends downwardly and is secured to the shaft floor. In addition, a counterweight rope extends from the plunger, over a pair of sheaves located at the top of the elevator shaft, to a counterweight. With this roping arrangement, the car will move twice the distance of plunger movement.
U.S. Pat. No. 5,056,627 discloses another example of a roped hydraulic elevator with a single jack located beside the car. A first rope is attached to the car, extends over a sheave located at the upper end of the plunger, and then extends downwardly and is connected to one end of a lever which is pivotally secured to the jack cylinder. A compensation rope is connected to the opposite end of the lever. The compensation rope extends upwardly from the lever over a first sheave secured on the top of the car. The compensation rope then crosses the top of the car, extends under a second car-mounted sheave, and then continues upwardly to the top of the shaft, where it is secured.
U.S. Pat. No. 5,238,087 discloses another roped hydraulic elevator. A car and a counterweight are attached to opposite ends of a rope, which is entrained over an idler sheave at the top of the elevator shaft. The counterweight, in turn, is connected to a drive rope, which extends around a pair of vertically spaced pulleys carried on a common tube. The ends of the drive rope are attached to the elevator shaft, and a hydraulic jack is connected to the tube for moving the tube up and down. Due to the roping arrangement, there is a 2:1 ratio between the jack plunger movement and movement of the drive rope.
Another example of a roped hydraulic elevator is disclosed in U.S. Pat. No. 5,653,311. In this system, the bottom of thejack cylinder, rather than being secured to the shaft floor, is secured to the guide rails. A rope has one end secured to the car frame. The rope extends over a sheave mounted on the top of the jack plunger, downwardly to a second sheave mounted at the base of the jack cylinder, and then upwardly to the top of the plunger where it is secured. This roping system provides a 3:1 ratio between jack movement and car movement. As disclosed in the '311 patent, providing a roping arrangement where the distance of car travel is a multiple of the extension of the plunger is advantageous, because it reduces the length of the jack tube required to produce a desired range of car travel.
The foregoing proposals tend to require complex roping systems. It would be desirable to provide a roped hydraulic elevator which utilizes a single jack, counter-balances the weight of the car, and produces car movement which is a multiple of the jack extension, but which at the same time is less complex in design than the foregoing proposals.